CVRA (Club Vaudois de Robotique Autonome) is a group of students and engineers passionate about robotics. It is based in Renens, Switzerland. They needed a compressed air tank for their robot project that could hold 4 bar (400kPa) of pressure.
They made several 3d printed prototypes in PLA and were successful in the end with tank holding some 6,5 bar sealed with some acrylic coating.
Interesting experiment, but be aware that pressurizing plastic containers with gas can lead to serious explosion.
Here is the advanced prototype sealed with "Doc Blue" sealant pressure tested under water:
Project homepage with extensive information and progression of development:
Here is the Hackaday post with lot of safety concerns and possible problems with this concept:
Stay safe kids!